How To Control The Fan Behavior Manually

Concept: A trip point and the fan speed

ODROID XU4 supports 3 cooling levels for thermal control, 0, 1, 2.
Level 0, which is the lowest level for thermal control and comes with the slowest fan speed.
And level 2, which is the highest level for thermal control and comes with the fastest fan speed.

Refer to this table.

Trip point

-

0

1

2

Temperature

0

60°C

70°C

80°C

Fan speed

0

120

180

240

This tables shows the default values that how the fan behaves. As this table shows, when the temperature reaches to 60°C, the target trip point will be changed to level 1 and the fan starts to run at 120 PWM value(0~255).
In the same vein, the target trip point will be level 3 and the fan runs at 240 PWM value when the temperature reaches to 80°C.

You can adjust the target trip points and its each fan speed as you want.
And even you can fix the fan speed at the constant speed you set.

Modify the trip points

Yes there're the other trip points named 3, 4, 5. But you can ignore them that we don't use. Same on thermal_zone4.
As we can see, each trip point at each thermal zone has same value 60000, 70000, 80000. That means each trip point is activated on 60°C, 70°C, 80°C.

Each trip point is editable by writing a custom value to the each trip point files set.
For example, if you want to set trip point 1 to be activated at 30°C, you can just write a value on them.